Fuchs, H.V.H.V.FuchsBrandstaett, P.P.BrandstaettHeizmann, M.M.HeizmannEckoldt, D.D.EckoldtRambausek, N.N.Rambausek2022-03-082022-03-082003https://publica.fraunhofer.de/handle/publica/305764The channel (1) contains perforated pieces (3) of different lengths. These are connected with chambers (4) outside the channel which form sound absorbers. The channels and or pieces are made of sheet metal, plastics, concrete or brick. The chambers can be cleaned periodically or continuously by fixed or movable nozzles (9). The chambers are connected with pipes (8) for cleaning agent via valves or other adjustments (7). ADVANTAGE - The sound absorber contains no acoustically active porous absorption material and is unaffected by dirt.de608624690patent1996-19612572